The present invention concerns a device for illuminating a limited, defined area (hereinafter called xe2x80x9clight fieldxe2x80x9d), e.g. cancerous tumours and other pathological skin conditions which can be treated by this method, comprising a light source with a reflector device together with light-conducting means. The device satisfies the demands for intensity and uniformity of the irradiation, while being so inexpensive, small, light and mobile that it can also be employed in the outpatients"" department.
Photochemical treatment has been shown to be a highly promising form of treatment for certain types of skin cancer, especially basal cell carcinoma, as well as some other skin disorders such as psoriasis. In this treatment a photosensitising compound, i.e. a substance which has little or no inherent toxicity, is applied to the tissue which is to be treated. Upon illumination highly reactive chemical species are produced, especially singlet oxygen. Thus, in subsequent illumination of the tissue the light-exposed cells which contain sufficient quantities of the photosensitising compound are killed. Certain types of photosensitising compounds, including certain porphyrins, have much greater affinity to cancerous tissue than to normal skin tissue. The treatment can therefore be directed specifically to the cancerous tissue, partly by means of the photosensitising substance""s greater affinity with such tissue and partly by directing the irradiation solely on to this tissue. This type of treatment is now in routine use in several hospitals all over the world.
For the photosensitising compounds in use to-day, light with a wavelength in the range 600-700 nm is normally employed. The amounts of light required for such treatment are relatively large, i.e. of the magnitude 50-100 J/cm2, which is normally supplied for a period of 5 to 10 minutes, i.e. with a fluence of approximately 100-200 mW/cm2. Laser light has therefore normally been used. Due to the high intensity required, very large lasers have to be employed, normally a Cu laser coupled to a dye laser set, e.g., at 630 nm. Lasers of this kind are very expensive both with regard to purchase and operation, they require specially trained personnel and they are not mobile. Since photochemical treatment of skin diseases is preferably carried out in the outpatients"" department and generally outside hospitals, there is a need for a light source which is inexpensive, can be used without extensive training and is easy to move. Furthermore, it is important for the area which is irradiated to be sharply defined, thus avoiding exposure of surrounding tissue. In addition, it is important that the fluence of the light should be approximately constant across the entire light field. Attempts have been made to replace the laser with a conventional light source, preferably a halogen lamp. However, it has proved difficult to combine high light intensity with uniform irradiation over a sharply defined and sufficiently large light field. Moreover, the light distribution from such light sources will be highly dependent on precise positioning of the incandescent element to the mirror or other optical device which collects and focuses the light, since the large aperture which this optical device must have in order to collect a sufficiently large portion of the light entails the necessity for a very high magnification. Since the mechanical reproducibility of halogen lamps is limited, this entails a not inconsiderable readjustment of the optics/lamp when the lamp is replaced. The invention which is described herein solves this problem as well as fulfilling the said requirements for intensity and uniformity of the light field. Furthermore, it enables the size of the light field to be varied in a simple manner.
The invention is characterized by the features which are presented in the independent claim 1 together with the dependent claims.